Issue
Unable to get modbus to communicate with the automation server and LC&D GR2400 lighting controller.
Environment
Modbus
Automation server
LC&D
GR2400
SmartStruxure Solution 1.5
Cause
The LC&D GR2400 lighting controller will ONLY allow 1 stop bit in it's modbus communication. Normally the stop bit setting in a modbus slave device is an "at least number", meaning the GR2400 should except 1 or more stop bits, but it does not.
The problem comes from the automation server by default sends the 1 stop bit and addition "guard bits" for modbus communication. The guard bit setting was not available in versions prior to 1.5 and by default the automation server would send 3 stop bits causing the modbus communication to fail with the GR2400lighting controller.
Resolution
- In SmartStruxure 1.5 right click on the Modbus Master Network and select properties.
- Click the advanced tab:
3. Here you see the guard bit setting. This value should be a 0 if the automation server is to ONLY send 1 stop bit. If this number is left at default the automation server will add the number of guard bits to the user setting of stop bits. By default that makes 3 stop bits from the Automation Server.
To properly communicate to the GR2400 the guard bit setting should be a 0 and the user selected stop bit should be a 1 in order to ONLY send 1 stop bit.
